1. Field of the Invention
The present invention relates to a method of measuring the deformation capacity(deformability)of microscopic objects, more particularly, of living cells such as red blood corpuscles.
2. Description of the Prior Art
It is known that the deformation capacity of red blood corpuscles plays an essential role in their functions and their time of survival. It is this capacity which enables these generally discocytic cells having a diameter on the order of 8 microns to pass through the capillary vessels having a diameter on the order of 2 to 3 microns.
Numerous methods of measuring the deformation capacity of red blood corpuscles have been proposed. In particular, it is possible to cite measurement of the relative negative pressure required to suck a portion of the cell into a micropipette, measurement of the elongation of the cells adhering to a surface under the action of a liquid flow or measurement of the time required for a specific quantity of cells to pass through a filter having calibrated microscopic pores.
All these methods, with the exception of the second method have the disadvantage that the forces acting on the cells are not well defined. In the case of the second method, the deformation of the cells depends partly on the manner in which they adhere to the surface. In addition, it is necessary to measure the elongation cell by cell. Accordingly, considerable time is required to obtain statistical data on a large number of cells.
Another known method of studying the deformation of red blood corpuscles consists in placing a sample of liquid containing these corpuscles in suspension between two coaxial walls driven at different speeds of rotation with respect to their common axis in the manner of the walls of a rotary viscometer having coaxial cylinders. This method makes it possible to accurately determine the fluid stresses which are exerted on the corpuscles by virtue of the gradient of the rotational speed. However, even with this method, the deformation of each cell must be measured individually after fixing the cells in the deformed state and examining them under a microscope. Accordingly, a considerable amount of time is required for this operation.
Lastly, it is also known that the average dimensions of very small objects such as specks of dust or droplets can be measured by an optical diffraction method. This method has also been used to determine the average diameter of red blood corpuscles, but it has not been employed to measure cell deformability under dynamic conditions.
It has been found that if a group of microscopic objects which initially are spatially distributed in an arbitrary manner, become aligned, change their shape and dimensions under the action of applied forces, the diffraction patterns which are obtained reflect these changes in shape and dimensions. If the sample under examination contains a mixture of different particle types the patterns obtained represent a combination of the patterns which would be produced by each of the individual types.